1. Field of the Invention
The present invention relates to data processing systems in general, and, more particularly, to credit schedulers for ordering the execution of tasks on a processor.
2. Description of the Related Art
In a data-processing system, when two or more operating systems operate on one piece of hardware, the tasks associated with each operating system contend for the hardware that is available. Without something to mediate their access, one operating system's tasks could monopolize or over-use the hardware to the detriment of the other operating system's tasks. When the hardware comprises more than one processor that is available to execute the various tasks, one processor can become over-utilized while another remains under-used. Therefore, a program that sits between the operating systems and the hardware acts as a mediator. This program is commonly known as a “hypervisor.”
One of the jobs performed by the hypervisor is to choose a processor that is to execute one or more tasks. Another job of the hypervisor is to schedule the order of execution of tasks. Another job of the hypervisor is to allocate the share of time that the data-processing system is to spend executing certain types of tasks relative to other types. These are not easy jobs. Some tasks are time-sensitive (e.g., tasks associated with input or output, speech processing, video processing, transmission or reception of signals, etc.) and some tasks are non-time-sensitive or are less time sensitive. Some tasks require relatively long times on a processor and other tasks requires less time. Whatever the mix, the respective operating systems are always presenting to the hypervisor tasks to be executed. If the hypervisor does not properly balance and allocate resources, the performance of the entire system can degrade. For voice- and media-related applications, the degradation is evidenced by poor quality of voice or video.
A need therefore exists for a hypervisor that can properly manage a complex mix of contending tasks, including time-sensitive and non-time-sensitive tasks.